Process for concentration of soluble electrolytes



April l5, 1958 G. MILLER ErrAl. 2,830,878

' PROCESS FOR CONCENTRATION OF SOLUBLE ELECTROLYTS co/v/vmATED /NVENTGRS GEORGE MILL E( er M @gis-wirf Apnl 15, 1958 G. MILLER Erm. v2,830,878

` PRocEss Foa CQNQENTRATION oF soLUBLE ELEcTRoLYTEs Filed Aug. 5. 1950 3 Sheets-Sheet 2 l sono l l Z April l5, 1 958 G. MILLER ETAL 2,830,878

lPROCESS FOR CONCENTRATION oF soLUBLE ELEcTRoLYTEs Arrks.

ionexchange.

lduction of potable `water from the sea.

`new raw resourcesland useful sans CONCENTRATION or SOLUBLE nLncrnoLrrEs y;

GeorgeMiiler, -arrantihilln Colombia, and

A Frank C. "Godfreyyoston, Mass.

Application August 5, 1950.5` silalN'o. 177,886` 4 claims. (oma-iso' Pnocnssron This invention relates -to `the concentrati-on of ionized soluble electrolytes; including acids, bases andsalts, by

The invention is useful, for instance, inthe production of industrial chemicals, in refining processes such as-` for l sugar, `in processing alcoholic beverages, in the desalting nature arecommerciallyuse ful.L "These are only a few of the uses to which the invention-may lbe putasvwill be apparent from the description. It makes available many processes which may [be based onit. l

Essentially the invention is an ion exchange process which takes advantage of the property .ofcertain ionizable compositionspwhich we have discovered can be produced 4 `byionjexchange,` of having, substantial variation in solur `bility with slight variations intemperature.

The inventive'processjcompriscsremoving anelectrolyte from a solutionof thesameandreproducing `saidelectrolyte in. a second solution `in order to convert aWweak solution of such ,electrolyte into la stronger solutionV of thejsarneor to forma substantially puresolution of(J such electrolyte from `a solutiorilof fthe same; containing irn-v purities and "othersoluble'compounds. This is done iby t `passing "such first solution' through anion exchanger having an. ion `capable of combining Awith an Vion in such .electrolyte to ,forni a` compound which is highly l'water soluble at one temperature andhighly Water insoluble at a lower temperature, thereby forming a solution of such compound and converting the ion exchanger into an ex- 4hausteld Yform` having' as exchangeable ions the remaining jions" of ,such electrolyte, precipitating such :compound `from such solution `v`thereof by maintaining the temperature of the solution belowftheprecipitation point of the compound Jfrornsuch solution, dissolving such `precipitate in water at atemperature atwhich the Ysa1ne issoluble United states Pamo" u A2,839,878 Patented Apr. 15, 1958 ice " 2 the claims is not intended to be -limited to the illustrative examples :contained in the description and in the schematic drawings more clearlyillustrating the process, of which Figrl is a schematic `diagram of anion exchange process for concentrating sodium hydroxide. s Fig. 2 is a schematic drawing of an ion exchange process for converting one electrolyte to another more suitable b for concentration purposesaccording to` the invention.

. Fig. 3 is a schematic diagram of part of the process t for `producing potable jwater and concentrated sodium hydroxide from sea Water according to the invention.

Fig. 4 isa schematic diagram of anlanion Yexchange concentration process ofthe invention.

Fig. 5 is a schematic diagram of an anion exchange process for regenerating a hydroxide form of exchanger as used in the invention. j

Fig. 6 isla schematic ldiagram of `an anion exchange process Vfor isolating and concentrating one of several salts in a solution. t v

Figs. 7 and 8 are schematic diagrams showing a chromatic or 4cascading ion exchange .concentration process.

Fig. `9 -is a schematic diagram of an alternativeprocess for concentration of magnesium chloride from sea `water by ionlexchange.

` Fig.V l0 is a schematic diagram `of a process for prolucing fa concentrated sodium vhydroxide from euent of theprocessf Fig. 9. p l

t is-ja schematicdiagram of a process for conversion and .concentration of an electrolyte using mixed exchangers i GENERAL DESCRIPTION `charged hydroxyl ionor anion OH*. `In solution, these ions (cation and anion). have the property of being able to separate or disassociate and to associate themselves with other oppositely charged ions Vfrom or in another substance or composition present in or in contact with the solution. This process is ion exchange and the other substance exchanges a similarly charged ionin .return for the ion which becomes associated with it, which may associate itself with an ,oppositely charged ion of the first composition. This process isanalogous to the exchange of partners between two couples on a dance oor.

An ion Vexchangeris any compositionor substance `which is capable of exchanging one of its ions either cation or in suchwaterland Aregenerating the exhausted exchanger vwiththe `solubilized precipitate, producing as an' exchanger 4effluent the second electrolyte solution.` Infthe event that itis desired `totorm amore concentrated solution of the electrolyte,` the amount of water used to dissolve the "precipitate `should `be less than'the amount qfgwater in? 'theoriginalrst electrolyte solution andthe temperature t should be-:such that thepprecipitate is ,soluble insuch 4an possibilities git'jmaltes`A apparent "andrthe scope iof Vcontact with it and it may be anion, `for one of thesirnilarly charged ions of the composition insolution whichiis passed through and incontact with the ion exchanger, `for convenience called the ex changer. i

An exchanger for the purposes of thisinvention is a massor quantity of an insoluble and `permanent material, usually-in a granulated, pea, saddle or other relatively divided form, and lying in a batch or bed so arranged `as in a tank Vthat'solutions can be passed through andvin Veither a cation exchanger or an anion exchanger.

The invention can perhaps be best understood in its general principles by the following simple example:

If a strontium Srcation is combined with two hydroxyl OH? ions, the composition strontium hydroxide Sr(OH)2 is `formed. This 'composition has the property that at a comparatively low'temperature it forms avsolid precipitate, but at a comparatively higher temperature vit forms a solution. Therefore, if two compositions one containing the hydroxide ion and the other the strontium ion in comparatively weak concentration are brought together in great quantity and at a low temperature, a great deal of the strontium hydroxide will be formedas a solid precipitate. Thereafter, if a small amount of water at elevated temperature is passed through the solid precipitate strontium hydroxide, the precipitate will become solubilized in a high concentration.

We have discovered that this process can be brought about, by ion exchange.

Generally speaking, any suitable ion exchangers may be used in the process of our invention which are in or may be exchanged into the form of the ion capable of exchange with ions of the raw material composition involved to form a precipitate having the desired temperature soluble properties. The invention is adaptable to the use of cation or anion exchangers.

The recently developed synthetic resin exchangers from which may be selected those best for the particular process involved according to readily available data are at present most satisfactory, for instance, the sulphonated copolymers of phenol and formaldehyde and the like which are available on the market under the trade name Amberlite such as the cation exchangers Amberlite IR-lOS, a sulphonicacid type, Amberlite IRC-50, a

carboxylic acid type, Amberlite 120, a sulphonic acid type, and among the anion exchangers Amberlite IRA- y 400, astrongly basic type.

It will be understood that the ion exchangers, particularly the synthetic resin ion exchangers discussed are well known and that a suitable exchanger maybe selected fromamong such readily available exchangers according to publicly available table data, and their complicated chemical formulas and compositions for the most part need not be dealt with here. For our purposes the cation exchange materials by themselves may be designated by R and the anion exchange materials by themselves may be designated Rx. Throughout the process of this invention a resin cation exchanger when it is used will be in the form of a metallic resinate, for instance, a strontium resinate SrRZ which is interchangeable in form as the process of cation exchange takes place and the anion exchangers when used will be in interchangeable forms of resin bases or salts, for instance, resin hydroxide RXOH or 'resin oxalate Rx2C2O4.

Thus, we may start with an ion exchanger in the strontrum resinate form SrR2 and if we pass sodium hydroxide NaOH through it at a comparatively low temperature the sodium ion Na will exchange with the strontium ion Sr converting the exchanger to the sodium resinate form NaR and producing a solid precipitate strontium hydroxide Sr(OH)2 which remains as a solid interspersed in the exchanger and also producing as eduent from the exchanger electrolyte-weakened water. Alternatively, instead of forming the precipitate within the exchanger, we may pass sodium hydroxide at an elevated temperature throughthe exchanger, thus forming the strontium hydroxide as a solution which passes out as effluent, and then forms the solid precipitate by cooling outside the exchanger.

Acompartively small amount of water applied to the precipitate either inside or outside the exchanger will solubilize it at a comparatively high concentration. `This concentrate, when passed through the exhausted 6X- changer, regenerates the latter to the original form and produces the original solution as concentrated eluent.

Example 1,-Concentration of sodiumy hydroxide A metal resinate, in the form preferably of the alkali-earth metals strontium or barium when combined with sodium hydroxide at reduced temperature produces a hydroxide of the metal involved, for instance strontium hydroxide Sr(OH)2 as la solid precipitate and converts the exchanger to the sodium form NaR. Such a precipitate is highly soluble at elevated temperature. 'l i Referring to Fig. 1, in a first run cool sodium hydroxide NaOH is fed through a line 12 and passed through a strontium resinate SrR2 form of exchanger in a suitable exchanger tank or apparatus indicated at 10, converting the exchanger to the sodium form NaR and producing the precipitate strontium hydroxide which remains interspersed in the exchanger as a solid, and electrolyteweakened water is produced as elfluent through a line indicated at 15. For the sake of clarity, the rst run and its reactions are shown at the left and subsequent runs on the right throughout the drawings. It will be understood that suitable line and valve arrangements can be made to accomplish the desired runs. When the exchanger is completely exhausted to the sodium form NaR so that no more strontium hydroxide precipitate can be produced, the sodium hydroxide feed through the line 12 is shut off and in a second run water H2O, at a temperature which is elevated to the temperature of solubility 'of the strontium hydroxide is introduced to the exchanger through line 12a. This immediately dissolves the strontium hydroxide and causes a reexchange to take place with the sodium resinate NaR form of exchanger, regenerating the exchanger back to the original strontium resinate SrR2 form and producing concentrated sodium hydroxide as effluent through the line 15a. It may be desirable to run the hot water back through the exchanger in the opposite direction, that is, into line 15a and out of line 12a.

The equations for the reactions taking place in the above process are as follows:

For continuous production, the exchange process is alternated between the sodium hydroxide first run and the hot water second run.

Example 2,-Concentraton of sodium chloride It may be desirable to concentrate a desired electrolyte conveniently by the process of Example 1 where, however, the electrolyte to be concentrated does not have an ion which in the concentration process of Example 1 forms a temperature soluble precipitate. In such case, the electrolyte desired to be concentrated can rst be converted to another electrolyte which has an ion capable when combined with the ion carried by the exchanger being used of forming the desired precipitate. Such an example is sodium chloride NaCl.

Referring to Fig. 2, the sodium chloride NaCl is fed through a line 16 into an exchanger tank 13 containing the anion exchanger resin hydroxide RxOH. The chloride ion exchanges with the hydroxyl ion of the exchanger converting the exchanger to the resin chloride RxCl form and producing sodium hydroxide NaOH as eluent through the line 19 in a first run. The sodium hydroxide is passed then into the line 12 in the rst run in the apparatus of Fig. 1 producing the solid precipitate and effluent water and in the second run of Fig. lthe concentrated sodium hydroxide which is then passed from the line 15a into the line 20 of Fig. 2 in a second run, producing from the line 19a the sodium chloride as effluent end product and reconverting the resin chloride form of exchanger back to the resin lhydroxide form ready for a succeeding rst run through the tank 18.

In this process the end effiuent sodium chloride from the line 19a is concentrated because the sodium hydroxide fed into the line 20 from the line 15a of Fig. 1 is also concentrated. In this process also the water eiuent from the line 15 may be so electrolyte-weakened as to be potable, depending upon the temperature of the sodium hydroxide fed into the line 12, Fig. 1.

The equations for these reactions are as follows:

` (3) srtoHn-y-zNaRepHzo geen (6) 3NaCl (conc.) -l-MgRz run producing concentrated sodium the line 3S.

`Copper ammonium hydroxide Cu(NH3)2(OH)2 is now` SrR-l-ZNaOH l(concentrated) where Rx is anion exchanger and R is cation exchanger.

Example 3.-C'oncentrati0n- `of several` salts in solution (sed water It may be desirable to'` concentrate several salts in a solution and;` to produce: electrolyte-weakenedor potable Water, for instance, from seawater. o

Assuming for illustrative, purposes that the composition of'sea water is a mixture of sodium chloride and magnesium. chloride,- and. referring to. Eig; 3, the mixture NaCl and MgCl2 is passed.` inaatrst run through aline mainte.. an exchanger tank 22 containing the sodium Nalformof resin. rlhe-magnesium chloride exchanges with; theY sodium resi'nate` to' form magnesium` resinate MgRg and. pure sodium` chloride NaCl as euent through the line. 24. Erom the line. 24 the sodiumrchloride is fed;` into the line 160i Fig.. Zinairst runto form sodium hydroxide efuent. from the -line. 19 which is then, conu centrated by feeding it into the line `12 oilig.A l according, to Example l.v The. 'concentrated .sodium` hydroxide euent. from thesline` 15a `islpassedthrough the `line. 20

in FigrZ producing eoncentrated-sodinmf chloride yNaCl euent fromthe `line 19d-of` L2 according to Example 2, which is then fedi'11-"al lsec runY through the; line 26 ofFig. 3 through the magnesium resinate MgR2 form of exchanger, re-exchanging 'theflatter back tothesodium NaR form. and producing thefiiiagnesium chloride and sodium chloride mixture of theoiiginal solution` but Vin concentrated form through the1ine2`8mFig. 3;

The. equations for, this example are as'follows;

MgCl2 (conc.) +NaCl+2N Example 4.-C0ncentraled `sodium hydroxide and electrolyte-weakened water from sea water Itimay be desirable to obtain from seawater or other mixed salt solution concentrated sodium hydroxide and water which can be made` potable, `and the process is illustrated` in Fig. 4, taking sea, WaterV for this purpose to be comprised of sodium chloride NaCl and magnesium chlorideMgClg." This mixture of salts is fed `throughay line into` an exchanger tank-32` container a resin hydroxide form of exchanger. The exchanger becomes resin chloride RxClQa solid precipitate magnesiumihydroxide MgQQl-Dz is `produced interspersed and remaining in "the exchanger and sodium hydroxide NaOH is the effluent through the line 34. The latter may then be concen- `trated `asV in Example liby feeding it into the line 12 of the exchanger tank 1'0in` Fig.V l1 and after the, second hydroxide through the lineilSrz; Fig. 1. p

Now the solid precipitate magnesium hydroxide must be dissolved out of the exchanger andthe exchanger regenerated back to the resin yhydroxide form. For this purpose,V copper ammonium chloride Cu(NH3)2Cl is fed into the resin chloride form of exchanger in a second run through aline 36 which leaves the exchanger `still in the resin chloride form but `produces ,thesolid precipitate copper hydroxide Cu(OH)2Vin `theexchanger and magnesium chloride and free ammonia as eftluent through ffermo thefresin chloride exchanger and copper hydroxide precipitate in a third run through the TUI line 40, regenerating the exchanger back tothefresin hydroxide RxOH form ready forV theiirst run, dissolving the copper hydroxide and. producing as effluent through the line 42 copper ammonium chloride Cu(NH3)2Cl.` The copper .ammoniurn chloride for thef second run may be led from the'tline'. 42 directly back into'the line Soand the remainder may be passed into mixing apparatus 50 wherey calcium hydroxide Ca(OI-l)2 is introduced through the line .51 toY form calcium chloridev CaCl2V solution as eiuent through theA line'SpSand' the copper ammonium hydroxide Cu(NH3)2(OH)2 which is fed through the line` 40 for the third run.`

desired, the magnesium chloride etlluent from the line 38 in Fig; 4 can also beI concentrated by passing it progressively through the; exchangers, ofv Figs. 3,; 2 andyl and back again, lthereby converting itvrst` to sodium chloride, then to` sodium hydroxide which is. concentrated and then reconvertingjit to the magnesium chloridein concentrated form.A

The equations for: thev reactions of this example are as follows: v l

(il NaCl-I- MgCl2 -l-RxOH NaCl-I isconcentrated by process of Example 1..

Y form of exchanger.

cutoenwxelfrugelzazuus o) zxxcocuroninzsnf -cu(oH)+2N1-13+cac1, .izlwzmpi'e` .5i-Concentration, by anionV exchangel i hydroxide Sr(OH)2 is produced as euent through the line 63o.

The equations for thegabove reactions aresas follows:

SHCI-U2 (cold dilute)}Rx2C2O4- 2RxOH-l-SrC2O4g-I-Water (a) Hgo (hoourzaxoH-psrczo@ Sr(OH)2 (conc.) -i-RxzCOq,

Example 6,-Seprzration and concentratonofone of the salts in a mixture Fig. 6 ilustrates a process bywhich one of several salts in a solutioncan be isolated and concentrated at the same time. For example, a mixture in solution of sodium chloride NaCl and strontium chloride SrCl2 is passedina iirst run through the line 70 into a tank 75 containing resin hydroxide RxOH form ofexchanger. The exchanger `becomes resin chloride RxCl and strontium, hydroxide Sr(OH).2 is formed as a solid precipitate remainingv in the exchanger. The sodium chloride runs on through and out of the line 76 as eiuent. By passing hot water in aJ second run` through the line 70a the precipitate is dissolved thereby exchanging the resin chloride back to the resin hydroxide form of exchanger and producing as efuent through the line 76a concentrated strontium chloride.

The equations for this reaction` are as follows:

Example 7.-Chromatc or cascading concentration The previous examples have illustrated concentration processes by the formation of only one temperature soluble precipitate. Such single precipitate processes exchange and precipitate most but not all of the reactant solutions passing through the exchanger and the electrolyte weakened water efliuent is partially but not entirely pure.

Referring to Figures 7 and 8, the present example illustrates a method of removal and concentration of electrolytes with an extremely high concentration of the electrolytes and substantially pure water as eflluent. In such a method the solution to be concentrated is passed successively through a cascading or chromatic series of exchangers, all capable of combining with the electrolytes of the solution and forming precipitates having progressive temperature ranges of solubility.

This method may be illustrated in the concentration of a sodium chloride NaCl solution in which, referring to Fig. 7, the sodium chloride is passed in a rst run through a line 80 into an exchanger tank 82 containing resin bromate form ofexchanger RxBrO3. The exchanger reverts to a resin vchloride RxCl form producing sodium bromatel NaBrO3 as effluent through the line 84. Now referring to Fig. 8, the sodium bromate is passed from the line S4 and fed through a line 90 in a iirst run to an exchanger tank 92 containing successive layers of exchanger in the forms, respectively, cesium resinate CsR, barium resinate BaRz, and thallium resinate TIR. In passing through the cesium resinate, most of the solution is exchanged to sodium resinate NaR and precipitated as solid cesium bromate CsBrOa. The greatly weakened sodium bromate solution passes on through the barium resinate, exchanging the latter to sodium resinate and precipitating as a solid barium bromate Ba(BrO3)2. The almost dilute remaining sodium bromate solution hence passes through the thallium resinate exchanger which reverts to the sodium resinate NaR form, forming the solid precipitate thallium bromate TlBrO3 and finally resulting in substantially pure water as eluent through the line 95. Each stage may contain sodium ion in admixture with cesium, barium, or thallium.

At this point it may be stated that where the eluent water produced by concentration processes forming single precipitates, as illustrated by the previous examples,

.is not pure enough to be potable or otherwise useable for purposes requiring substantially pure water, a suitable chromatic or cascading concentration process as illustrated by the present method may be used.

In a second run through the exchanger tank 92 hot water in comparatively small quantities is fed through the line 95a in reverse direction with respect to the original order of the exchangers in the tank 92, successively dissolving the thallium bromate, the barium bromate, and the cesium bromate, regenerating the layers of sodium resinate successively to thallium resinate, barium resinate, and cesium resinate and producing through the line 90a as eiiiuent concentrated sodium bromate NaBrO3. The latter may then be fed through the line a into the tank 82 in Fig. 7, regenerating the resin chloride to the resin bromate RxBrO3 form and producing as end product efliuent through the line 84a concentrated sodium chloride.

The equations for the above reactions are as follows:

(2) Naro3 (cold, dimmi-CSR;

NaR+CsBrO3+NaBrO3 (more dilute) NaR-Ba(Br03)2-|NaBrO3 (still more dilute) NaR-i-TlBrOa-i-(pure water) TlR-i-NaBrO (hot, concentrated) (6) NaR-i-Ba(BrO3)2-{NaBrO3 (hot, concentrated)- BaR2+NaBrO3 (hot, still more concentrated) (7) NaR-i-CsBrOa-I-NaBrOa (hot, still more concentrated)- CsR}-NaBrO3 (fully concentrated) (8) NaBrO3 (conc.)+RxCl- RxBrOaNaCl (concentrated) Example 8.-Concentratz'on of magnesium chloride from l sea water Fig. -9 illustrates an alternative method for production of concentrated magnesiumV chloride from sea water according to the invention, taking sea water as comprising sodium chloride and magnesium chloride. The sea water is passed in a rst run through a line into a tank 102 containing resin iodate RXIO3 form of exchanger. The latter reverts to a resin chloride RxCl form and the solid precipitate sodium iodate'NaIO3 is formed in the exchanger, producing as effluent through the line 104 a solution of a more dilute form of sodium chloride and magnesium chloride which, in turn, is fed into an exchanger tank 106 containing a sodium NaR form of resinate producing magnesium resinate MgR2 and dilute sodium chloride as an eluent from the line 108.

In a second run a small amount of hot Water is passed through the line ltla into the tank 102 dissolving the sodium iodate, reverting the resin chloride exchanger to the resin iodate form and producing sodium chloride as effluent in the line 110 which is then fed in the second run into the tank 106, exhausting the magnesium resinate exchanger back to the sodium NaR form and producing in the line 112 the desired concentrated magnesium chloride.

The equations for the above reactions are as follows:

Example 9,-C0ncentratz'on of sodium hydroxide n lhe process of Example 8 The dilute sodium chloride from the line 108 in Fig. 9 may be passed through a line 115 Fig. 10 in a iirst run to an exchanger tank containing resin hydroxide form of exchanger. This exhausts the exchanger to the resin chloride RxCl form and produces as eluent through line 122 dilute sodium hydroxide. The latter is passed through the apparatus of Fig. 1 and treated according to the process of Example l to produce the end product sodium hydroxide.

The resin chloride exchanger is regenerated back to the resin hydroxide form in the tank 120 with any suitable hydroxide herein designated AOH passed through the line 124, producing as effluent a chloride designated AC1 in the line 126. The chloride AC1 may be recuperated in any suitable manner, as by treatment in apparatus 128 with a suitable hydroxide designated XOH introduced in the line 130 and with a waste eiiiuent chloride designated XCl from the line 132. Such a recuperation method is shown in the copending application of Godfrey filed March 31, 1950, Serial No. 153,219, now abandoned, and is also substantially the method of regeneration and recuperation illustrated in Fig. 4 of the present application.

Example ]0.-Smaltaneoas conversion and precipitation in mixture 0f exchangers In previous examples, for instance, in Example 2, Where f1 carried'outsimultaneouslywith aftormation of the vpreci'p` `ita'te in a,=single exchange step. usingfaV mixturez offexchangers which accomplish the desired result.

Referring to Fig. 1l sodium chloride which is to be lconf `centrated is fed in a rstrun through a line 140 into anV exchangertank 142 containing a mixture of thecation `exchanger cesium resinate CSR and anion exchanger resin bromate RxBrO3. Exchange ofthe sodium and chloride 3ions takes place simultaneouslyxwith the two forms of exchanger which become sodium resinate NaR and .resin v `-ch1oride RxCl thereby producing the solid precipitate i cesium bromate CsBrO3 and `electrolyte-weakened water as eiliuent throughthe line 144. When the exchanger has become thus` exhausted the usualV small amount of hot Water is nowfed into the line 1400i causing the exchangers to revert back to their original form cesium resinate and resin bromate andproducing concentrated sodium chloride as eiuent end product through the line M451.

Throughout` the aboyeexamples as illustratedin the drawings Vthe solid precipitates have beenshown as formed within and interspersed in the exchanger itself since the original solutions `were fedthrough` the exchangers `at temperatures whereby precipitation immediately took place.

. As mentioned above, however, if desiredthe precipitates may be formed as solids outside of the exchanger by passing the original solutions through the exchangers in the rst runs at temperatures of solubility of the precipitates. This causes the solution ofthe desired precipitates to pass out of the exchangers in the efuent after `which precipitation can be broughtv about by subjecting the eiuent to a temperature differential, usually cooling.` In such cases i the usually hot water used for concentration purposes is first introduced to the precipitate causing the latter to i solubilize after which the resulting solution is passed back through the exchanger to form the desiredv original electrolyte in concentrated form.

Where the cascading or chromatic concentration process is` used, if it is desired to Vform the solid precipitates outside of the exchangers these precipitates may be formed between stages ofthe concentration process.

It will also be understood that when the cascading concentration process is used, the electrolyte eiuent from each successive stage may be converted to another more desirable electrolyte before it is passed into a succeeding stage for the formation of av temperature soluble precipitate of decreasing solubility.`

We claim: e

1. The process of concentrating an electrolyte solution comprising the'step of passing a iirst solution of said electrolyte through a solid ion exchanger bed having exchangeable ions which form with one of the ions of said electrolyte a compound which is highly water soluble at i elevated temperatures and highly `waterinsoluble at lower temperatures, thereby producing a solution of said comi pound and converting said exchanger to an exhausted form having as exchangeable ions `the remaining ions ot second solution of said compound, and then `passing i through said exhausted exchangerfsaid second solution of said compound, thereby producing a `second solution of i `said electrolyte which is more `concentrated than said i saidJirs e1 l `a compound which is highly water soluble at elevated temperatures and highly water insoluble at lower temperatureshthereby producing said compound and converting said exchanger to an exhausted form having as f exchangeable ions the remaining ions of said electrolyte, maintaining the temperature of said iirst electrolyte solution while being passed through said ion exchanger bed `at a temperature which is suiciently reduced to precipitate said compound as a solid from said solution thereof, whereby said compound is precipitated as a solid upon jsaid ion exchanger as said solution thereof is formed, passing water in an amount smaller than the amount of water contained in said rst electrolyte solution and at a temperature which is sufficiently high to dissolve said precipitated compound in said smaller amount of water, through said exhausted ion exchangerV with said compound precipitated thereupon, thereby dissolving said precipitated compound and forming a second solution thereof which regenerates said exchanger to its original form and produces a second electrolyte solution Awhich is more concentrated than said iii-st electrolyte solution.

3. A process for concentrating an alkali metal hydroxide solution comprising passing a first solution of said "alkali metal hydroxide through a cation exchanger in the form of a resinate of an alkaline earth metal selected from the group consisting of barium and strontium, to produce a solution of the hydroxide of said alkaline *earth metal and converting said alkaline earth metal resinate into an alkali metal resinate, precipitating as a solid said alkaline earth metal hydroxide from said solution thereof by maintaining the temperature of the same at a` temperature suiciently reduced to cause precipitation of saidfcornpound as a solid from said solution,

i* dissolving said precipitated alkaline earth metal hydroxide in an amount of water which is less than the amount of water contained in said rst electrolyte solution and at a temperature which issufficiently high to dissolve said precipitated compound in said lesser amount of water,

4. A pro-cess for concentrating an alkali metal hydrox-v` ide solution comprising passing a iirst solution of said alkali metal hydroxide through a cation exchanger in the form of a resinate of an alkaline earth metal selecting from a group consisting of barium and strontium to produce a solution of the hydroxide of said alkaline earth metal, and converting said alkaline earth metal resinate into an alkali metal resinate, maintaining the i temperature of said rst solution of said electrolyte while being passed through'said cation exchanger bed at a temperature suiciently reduced to precipitate said alkaline earth metal compound from said solution thereof, whereby said alkaline earth metal hydroxide is precipitated as a solid upon said ion exchanger as said solution thereof is formed, passing water in an amount less than the amount of water in said iirst electrolyte solution and at a temperature which is sutliciently high to dissolve said precipitated alkaline earth metal hydroxide in said smaller amount of water, through said exhausted ion exchanger with said alkaline earth metal hydroxide precipitated thereupon, thereby dissolving said alkaline earth metal hydroxide and forming a second solution thereof, which regenerates said alkali metal resinateion exchanger back to its original form of said alkaline earth metal resinate and produces a second solution of said alkali metal hydroxide which is more concentrated than said rst solution thereof.

References Cited in the le of this patent UNITED STATES PATENTS Trump May 21, 1912 Russberg Apr. 7, 1931 Hunter et al. Oct. 22, 1946 Bauman Aug. 5, 1952 

1. THE PROCESS OF CONCENTRATING AN ELECTROLYTE SOLUTION COMPRISING THE STEP OF PASSING A FIRST SOLUTION OF SAID ELECTROLYTE THROUGH A SOLID ION EXCHANGER BED HAVING EXCHANGEABLE IONS WHICH FORM WITH ONE O THE IONS OF SAID ELECTROLYTE A COMPOUND WHICH IS HIGHLY WATER SOLUBLE AT ELEVATED TEMPERATURES AND HIGHLY WATER INSOLUBLE AT LOWER TEMPERATURES, THEREBY PRODUCING A SOLUTION OF SAID COMPOUND AND CONVERTING SAID EXCHANGER TO AN EXHAUSTED FORM HAVING AS EXCHANGEABLE IONS THE REMAINING IONS OF SAID ELECTROLYTE, MAINTAINING THE TEMPERATURE OF SAID COMPOUND AT A TEMPERATURE AT WHIH SAID COMPOUND PRECIPITATES AS A SOLID, THEREBY PRECIPITATING SAID COMPOUND AS A SOLID, DISSOLVING SAID PRECIPITATED COMPOUND WITH AN AMOUNT OF WATER WHICH IS SMALLER THAN THE AMOUNT OF WATER IN SAID FIRST ELECTROLYTE SOLUTION AND AT A TEMPERATURE WHICH IS SUFFICENTLY HIGH TO DISSOLVE SAID PRECIPITATED COMPOUND IN SAID AMOUNT OF WATER, THEREBY FORMING A SECOND SOLUTION OF SAID COMPOUND, AND THEN PASSING THROUGH SAID EXHAUSTED EXCHANGER SAID SECOND SOLUTION OF SAID COMPOUND, THEREBY PRODUCING A SECOND SOLUTION OF SAID ELECTROLYTE WHICH IS MORE CNCENTRATED THAN SAID FIRST SOLUTION OF SAID ELECTROLYTE AND REGENERATING SAID EXCHANGER TO ITS ORIGINAL FORM FOR USE REUSE FOR PASSING MORE OF SAID FIRST ELECTROLYTE SOLUTION THERETHROUGH. 